2.55, 2.56, and 2.57 are practice exercises.

2.58. Solution is not unique.

int is_big_endian()
{
  int a = 0xf0000000;
  char *b = (char*) &a;
  return *b != 0;
}

2.61.

A) !!x
B) !!~x

Assuming ints are 4 bytes:
C) !!(x & 0xff000000)

Without the assumption:
C) !!(x & (0xff << (sizeof(int)-1)*8))

D) !!(~x & 0xff)

Extract bit n.

int testn(int a, unsigned int n)
{
  return (a & (1 << n)) != 0;
}

void set(int* a, unsigned int n)
{
  // This will not be compiled as / and %.
  unsigned int position = n / (8*sizeof(int));
  unsigned int offset   = n % (8*sizeof(int));
  a[position] |= (1 << offset);
}

void reset(int *a, unsigned int n)
{
  unsigned int position = n / (8*sizeof(int));
  unsigned int offset   = n % (8*sizeof(int));
  a[position] &= ~(1 << offset);
}